Numerical analysis of the deep soil failure mechanism for perimeter pile groups

In this paper, the lateral limiting pressure offered by the deep ‘flow-around’ soil failure mechanism for perimeter (ring) pile groups in undrained soil is explored using two−dimensional finite element modelling. A parametric study investigates the role of group configuration, pile−soil adhesion, group size, pile spacing and load direction on group capacity and corresponding soil failure mechanisms. The finite element output show that the plan group configuration (square or circular) has a negligible influence on lateral capacity for closely spaced perimeter pile groups. When compared to ‘full’ square pile groups with the same number of piles, the present results suggest that for practical pile spacing (≳ two pile diameters), perimeter groups do not necessarily increase capacity efficiency, particularly if the piles are smooth. Nevertheless, perimeter groups are shown to be characterized by both the invariance of their capacity to the direction of loading and their highly uniform load-sharing between piles, which are beneficial features to optimize design.

Interpretation of uplift pipeline-soil interaction behaviour using acoustic emission measurements

The objective of this study was to develop quantitative acoustic emission (AE) interpretation for uplift pipeline-soil interaction behaviour, enabling early warning of serviceability and ultimate limit state failures in the field. A series of large-scale uplift experiments was performed on a steel pipe in sand with different burial depths (i.e., stress levels), and varying rates of deformation were imposed. A suite of AE parameters was compared with the pipe force and displacement behaviour. Image-based deformation measurements were used to monitor the soil displacement field. AE generation was proportional to the imposed stress level and pipe displacement rate and related to the evolution of the pipe/soil failure mechanism. Relationships have been quantified between AE generation and stress level (R2 values of 0.99), and between AE generation rate and pipe velocity (R2 values ranging from 0.95 to 0.98), enabling interpretation of accelerating deformation behaviour that accompanies progressive ground failure processes. An example interpretation framework demonstrates how AE parameters can be used to identify the mobilisation of peak uplift resistance and quantify accelerating deformation behaviour during post-peak softening.

Research Status and Prospect of Seepage Erosion in Foundation Pit Engineering

In water-rich strata, the distribution of groundwater is complicated. Construction projects related to foundation pit engineering in such areas are prone to cause piping failure, fluid soil failure, and other seepage-related failures. Seepage erosion is a kind of seepage failure that occurs inside the soil. Because the process is difficult to observe and measure, seepage erosion is rarely considered in the current foundation pit engineering. This article analyzes the relevant research on seepage erosion, and further clarifies the influence of seepage erosion on soil characteristics. In addition, this article puts forward some suggestions for the shortcomings of the current research on erosion, and made some prospects for future research on erosion in foundation pit engineering, hoping to provide theoretical guidance and thinking inspiration for future research.

Biomimetic Rotary Tillage Blade Design for Reduced Torque and Energy Requirement

A rotary cultivator is a primary cultivating machine in many countries. However, it is always challenged by high operating torque and power requirement. To address this issue, biomimetic rotary tillage blades were designed in this study for reduced torque and energy requirement based on the geometric characteristics (GC) of five fore claws of mole rats, including the contour curves of the five claw tips (GC-1) and the structural characteristics of the multiclaw combination (GC-2). Herein, the optimal blade was selected by considering three factors: (1) the ratio ( r ) of claw width to lateral spacing, (2) the inclined angle ( θ ) of the multiclaw combination, and (3) the rotary speed ( n ) through the soil bin tests. The results showed that the order of influence of factors on torque was n , r , and θ ; the optimal combination of factors with the minimal torque was r = 1.25 , θ = 60 ° , and n = 240 rpm . Furthermore, the torque of the optimal blade (BB-1) was studied by comparing with a conventional (CB) and a reported optimal biomimetic blade (BB-2) in the soil bin at the rotary speed from 160 to 320 rpm. Results showed that BB-1 and BB-2 averagely reduced the torque by 13.99% and 3.74% compared with CB, respectively. The field experiment results also showed the excellent soil-cutting performance of BB-1 whose average torques were largely reduced by 17.00%, 16.88%, and 21.80% compared with CB at different rotary speeds, forward velocities, and tillage depths, respectively. It was found that the geometric structure of the five claws of mole rats could not only enhance the penetrating and sliding cutting performance of the cutting edge of BB-1 but also diminish the soil failure wedge for minimizing soil shear resistance of BB-1. Therefore, the GC of five fore claws of mole rats could inspire the development of efficient tillage or digging tools for reducing soil resistance and energy consumption.

Characteristic parameters of soil failure criteria for plane strain conditions – experimental and semi-theoretical study

The paper concerns the characteristic parameters of the selected isotropic failure criteria, i.e. Mohr–Coulomb, Drucker–Prager, Matsuoka–Nakai and Lade–Duncan. The parameters are determined directly from the failure criteria and stress measurements or by semi-theoretical approach, assuming that the soil obeys the associated flow rule and using the plane strain condition. In the latter case, the parameters can be expressed as functions of the plane strain internal friction angle, which is determined from measurements. The principal stress tensor components, corresponding to the soil peak strength and necessary to obtain the failure criteria parameters, are measured in a series of true triaxial, plane strain tests, on coarse Skarpa sand samples of different initial relative density, subjected to various confining pressures.

Sliding Mode-Based Traction Control for An Autonomous Martian Rover

A traction control system was developed for an autonomous Martian rover using a sliding mode controller. The main inspiration for this project was NASA’s Mars rover, Curiosity, which suffered severe wheel damage due to the lack of an effective traction control system. A control system was sought out to effectively prevent wheel damage, slippage, and soil failure for a Martian rover. It was initially hypothe-sized that a sliding mode controller would be most effective to control the vehicle’s traction. A Simulink model was created with a deformable soil-rigid tire mathematical model in order to simulate the traction control system. The sliding mode controller was tested to be more robust and stable compared to a proportional-integral-derivative (PID) controller for the rover. The results elaborate the possible applica-tions for this project, which spans across commercial and military rovers, rescue robots, and planetary rov-ers in the private and global space industry.

Experimental characterization of natural fibre–soil interaction: lessons for earthen construction

Earthen construction materials are the subject of renewed interest due to the rising alarm about environmental pollution from the construction industry. Current research efforts are focused on improving the mechanical properties of earthen materials to make them modern and competitive. To increase strength and improve ductility fibres can be added to the soil mixture and if natural fibres are used one achieves stabilisation in an environmentally friendly way. Several previous studies have dealt with the behaviour of this composite material at a macroscopic level and on the general interaction between fibres and soil, but there is little published research on the interfacial mechanical interaction between natural fibre reinforcement and a soil matrix which is key to the former. This paper attempts to fill this gap by presenting and discussing laboratory results from a large campaign of pull-out tests conducted on composite earthen samples. The variables investigated here are the nature of the fibres (i.e. single or collections twisted together) and the use of fibre treatments such as PVA glue and baking soda. In the study both fibre–soil failure and soil-soil failure are investigated and the results lead to conclusions as to appropriate use of fibres to reinforce earthen construction materials.

Plasticity and Strength Behaviour of Marine Clay Stabilized with Waste Steel Dust for Soil Improvement Works

Soft marine clay soil is characterized with highly compressible behavior, in which associated with poor bearing capacity and low in shear resistance. Soil improvement works are carried out to reduce the soil failure and destruction to the superstructure. Various techniques available for soil stabilization including the use of admixture to improve the engineering properties of the problematic soil. This paper aims to report on the use of waste steel dust retrieved from the medication supply industry as soil stabilization agent. Several series of Atterberg limit test and Unconfined Compressive Test were carried out to foresee the potential use of the waste steel dust for the purpose of civil engineering applications. The significant findings from this study is evident that the waste steel dust ranges from 5% to 15% did not able to serve as soil stabilization agent. It can reduce the plastic behavior of the soil sample; however, it also caused the strength of the soil declined. In comparison with previous studies, the presence of activated agent could possibly enhance the performance of waste steel dust as an alternative treatment agent to soil improvement works. The use of activated agent is to serve as pozzolanic materials to create cementitious bonding in between the soil interparticles matrix.

Modeling Soil Forces on a Rotary Tine Tool in Artificial Soil

HighlightsA mathematical model of soil reaction forces on a rotary tine tool was developed.Soil bin experiments using artificial soil enabled observation of soil failure due to soil-tine interaction.The model-predicted forces were similar to experimentally measured forces.Abstract. Understanding soil-tool interaction can enable better control of weeding tools to achieve higher weeding efficacy. The interaction between a vertical tine (mounted on a rotating disc) and soil was investigated using a mathematical model that estimated soil horizontal forces on the tine operating at different linear and rotational velocities. The kinematics associated with the linear and rotational velocities of the rotary tine tool were modeled, and the shearing and inertial forces were estimated. To evaluate model performance with different experimental factors, two sets of soil bin experiments were conducted using an artificial soil: with one tine to estimate model parameters and with two tines 180° apart. Experimental factors were longitudinal velocity (travel speed) at three levels (0.09, 0.29, and 0.5 m s-1) and speed ratio, i.e., the ratio of longitudinal velocity to peripheral velocity of the tines, at three levels (1, 1.5, and 2). Soil horizontal force and torque on the rotary tine tool were measured. A nonlinear least squares method was used to estimate model parameters from the experimental data, resulting in shearing force coefficients ranging from 2.9 to 37 N and inertial force coefficients ranging from 16 to 528 N s2 m-2. The variations in the shearing and inertial forces on the tine were due to differences in soil failure patterns among the treatments. The predicted longitudinal and tangential forces for two tines using the model showed trends that were similar to the forces measured in the experiment. However, the model overestimated the predicted forces because it did not account for the reduced force on a tine due to soil disturbance created by the other tine. Keywords: Soil-tine interaction, Weed control.